Multi-constellation GNSS Performance Study Under Indian Forest Canopy

GPS-based forest survey is being increasingly popular over the conventional methods; signals from other operational GNSS constellations are also being used for the purpose. The forest environment is different from the open-sky and urban environments as the type, height, density of the trees and the season-dependent foliage properties degrade the GPS/GNSS signals passing through the foliage within a dense multipath environment. This manuscript presents the results of a study on the solution quality of standalone and hybrid constellation GNSS (GPS, GLONASS, Galileo) operation within an Indian forest predominantly containing evergreen or dry-session deciduous Sal (Shorea Robusta) trees of the Dipterocarpaceae family, abundantly found all over India. The results show that in the single-frequency, static operation, single constellation GNSS solution quality degrades in comparison to open-sky operation with intense fluctuations in received signal strength reaching the GNSS antenna. Multi-constellation, hybrid GNSS operation improves the situation and GPS + GLONASS + Galileo provides better than 1.5 m horizontal (2DRMS) precision. The results of the study would be useful for the survey, especially for the forest survey community.